1. Field
Embodiments may relate to a wafer substrate bonding structure and a light emitting device comprising the same.
2. Background
A light emitting diode (hereinafter, referred to as LED) is an energy device converting electrical energy into light energy. The LED consumes low electric power and has a long life span. Therefore, the LED can be applied at a low cost.
As the advantages of the LED are becoming important issues, the LED is now widely used in various fields. However, due to the characteristic of the LED, high power application for high output has lower efficiency than that of low power application.
Therefore, a vertical type LED is now proposed which includes an efficient electric current application structure. Unlike a horizontal type LED obtained by etching a portion of a semiconductor layer and by forming an electrode in the etched portion, the vertical type LED is formed by placing directly an electrode on the top surface and the bottom surface of a semiconductor layer. Therefore, electric current can be efficiently applied from the electrode to the semiconductor layer. Accordingly, the vertical type LED achieves greater efficiency and greater power output than those of the horizontal type LED. Also, since the vertical type LED is cooled more easily than the horizontal type LED, the vertical type LED is able to easily radiate heat generated from the operation of the vertical type LED.
Meanwhile, since the electrode should be located on the top and the bottom surfaces of the semiconductor layer in the vertical type LED, the vertical type LED requires a different manufacturing process from that of the horizontal type LED. For example, after a semiconductor layer is grown on a growth substrate like a sapphire substrate, the growth substrate should be removed before subsequent processes are performed. Here, before the growth substrate is removed, the semiconductor layer is plated in advance or is wafer-bonded in order to support the semiconductor layer having no growth substrate.
In the wafer-bonding, due to the thermal expansion coefficient difference between the growth substrate like a sapphire substrate and a new bonding substrate, a crack may be generated in the semiconductor layer during a cooling process after the wafer-bonding process, and overall structure may get bent or twisted.
Accordingly, there is a necessity of developing a wafer substrate bonding structure, which is suitable to be applied to a wafer-bonding method of the vertical type LED, and of developing a light emitting diode using the same.